1. Field of the Invention
This invention relates to a method of and a system for entering identification codes into a vehicle antitheft system.
2. Description of Related Art
In order to cope with frequent occurrence of vehicle thefts in recent years, various vehicle antitheft devices and systems have been proposed. One of the vehicle antitheft systems is called an immobilizing system comprising an identification code dispatching key and an immobilizer unit which monitors an identification code (which is hereafter referred to as an ID code) dispatched from the key to prevent an engine controlling unit (EGI) from actuating the engine when an ignition switch is turned on in the event that the key is identified as incorrect based on the ID code. Such a vehicle antitheft system is known from, for example, Japanese patent application No. 6 - 181146, filed on Aug. 2, 1994, by the applicant of this application and now opened to the public as Japanese Unexamined Patent Publication No. 8 - 40206.
Another type vehicle antitheft system employs encoded words (which are hereafter referred to as CWs) for permitting the engine controlling unit (EGI) to actuate the engine as is known from, for example, Japanese patent application No. 6 - 297086, filed on Nov. 30, 1994, by the applicant of this application and opened to the public as Japanese Unexamined Patent Publication No. 8 - 150899. Specifically, the immobilizer unit compares an ID code of a key read in through a transponder with an ID code registered therein and transfers a word code, different in form from these ID codes, to the engine controlling uniy (EGI) whenever verifying the coincidence between these ID codes for another verification of the coincidence between the word code from the immobilizer unit and a word code registered in the engine controlling unit (EGI). The immobilizer unit transfers a permission command signal to the engine controlling unit (EGI) to permit it to actuate the engine only when the engine controlling unit (EGI) verifies the coincidence between these encode words.
With regard to a vehicle antitheft system of the type in which, when an ID code of an ignition key read in through a transponder coincidents with an ID code stored in an immobilizer, a command signal is transmitted to an engine controlling unit from the immobilizer to permit the engine controlling unit to perform control of the engine, it has been proposed in Japanese patent application No. 6 - 340176, filed by the applicant of this application that the vehicle antitheft system is shifted to an additional code entry mode for altering ID codes in the immobilizer unit and the engine controlling unit when different ID codes of ignition keys read through the transponder are coincident with ID codes stored in the immobilizer. This prohibits the vehicle antitheft system to shift to the additional code entry mode with only one approved ignition key, so as to improve prevention against theft of the vehicle.
In order for the conventional vehicle antitheft systems to shift to the additional code entry mode, it is generally simple to verify coincidence between at least two different ID codes. However, in the event, for example, where ID code entry operation is interrupted for some reasons before entry of an ID code of the second ignition key in the immobilizer unit and/or the engine controlling unit, because there is only one or no ID code registered in the vehicle antitheft system, it is impossible to resume the ID code entry operation even when the vehicle antitheft system is in the additional code entry mode or to shift the vehicle antitheft system to shift to the additional code entry mode for another entry of ID codes. Further, in the vehicle assembly factory where assembling operation must be strictly controlled according to a time schedule, manually shifting the vehicle antitheft system to the additional code entry mode which is usually complicated is troublesome and unpractical in view of working efficiency. In addition, when it is intended to enter a plurality of ID codes in the vehicle antitheft system, newly or additionally, it is possible to make a double entry of a same ID code.